Maybe Business is Not Your Thing, Young Man.

An old man is selling watermelons.

His price list reads:
1 for $3
3 for $10

A young man stops by and asks to buy one watermelon.

"That'd be 3 dollars", says the old man.

The young man then buys another one and another one, paying $3 for each.

As the young man is walking away, he turns around, grins, and says:

"Hey, old man, do you realize I bought three watermelons for only $9? Maybe business is not your thing."

The older man smiles and mumbles to himself:

"People are funny. Every time they buy three watermelons instead of one, they keep trying to teach me how to do business." 😁

(Story from Alvinfoo).